NASA astronauts Butch Wilmore and Suni Williams, who launched aboard Boeing's Starliner spacecraft to the International Space Station (ISS) in June, have reported a repetitive "pulsing sound" coming from the spacecraft, NASA confirmed on Monday.

The two astronauts called the NASA ground crew on Saturday asking for help with the sound, according to a U.S. media report, citing audio recordings between the astronauts and Mission Control in Houston.

"A pulsing sound from a speaker in Boeing's Starliner spacecraft, heard by NASA astronaut Butch Wilmore aboard the International Space Station, has stopped," NASA Commercial Crew said on X.

The feedback from the speaker was the result of an audio configuration between the space station and Starliner, according to NASA.

The space station audio system is complex, allowing multiple spacecraft and modules to be interconnected, and it is common to experience noise and feedback, NASA said.

"The crew is asked to contact mission control when they hear sounds originating in the comm system. The speaker feedback Wilmore reported has no technical impact to the crew, Starliner, or station operations, including Starliner's uncrewed undocking from the station no earlier than Friday, September 6," said NASA.

Boeing's Starliner spacecraft is scheduled to leave the ISS on Friday and return to Earth with no astronauts onboard.